This invention relates to a programmed shutter designed to provide suitable exposures by automatically setting, in response to the objective brightness, aperture and exposure time for actuating a driving mechanism for blades which serve both as diaphragm blades and shutter blades.
There have been several prior programmed shutters designed to automatically regulate suitable exposures. A typical one of these is an aperture-preset type programmed shutter which comprises a diaphragm mechanism driven by a driving actuator associated with a moving coil and a separate shutter mechanism. This type is designed to determine first the diaphragm aperture value, as is specified by the diaphragm mechanism, and then the shutter blades are opened under the abovementioned preset aperture value. After performing the exposure, the shutter is closed.
Another representative type of prior art employs common blades for shutter and diaphragm, but they are opened by a conventional governor mechanism, and when, in such opening process, the blades reach the determined aperture value, they immediately are closed.
In the first mentioned example prior art, i.e., the aperture-preset type, the driving actuator is associated with a moving coil of an ammeter. Therefore, its reaction to rapid changes of the object is too slow. For instance, if the object becomes suddenly bright or dark when determining the aperture value, there are possibilities of exposure errors occurring. This type of system has further shortcomings in that the employment of a moving coil limits the strength of the mechanism against impacts, and the dual installation of an intricate diaphragm mechanism on top of the shutter mechanism makes the combination very complicated.
In the second example of prior art cited above, the governor mechanism for controlling the blades has a very intricate and delicate constitution, and hence, in a long period of frequent use, the exposure performance is liable to deteriorate in precision.